Sulfited fatty compounds with a reduced content of free hydrogen sulfite

ABSTRACT

Sulfited fatty compounds having a reduced content of free hydrogen sulfite are prepared by blowing unsaturated fatty compounds in an oxygen atmosphere at 100° C. to 150° C., sulfiting the blown fatty compounds with sodium metabisulfite, and subsequently fixing unreacted hydrogen sulfite as sulfosuccinic acid ester by aftertreatment with maleic acid esters, and optionally, a basic material.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to sulfited fatty compounds with a reducedcontent of free hydrogen sulfite, to a process for their production, inwhich unsaturated fatty compounds are blown and sulfited and unreactedhydrogen sulfite is fixed as sulfosuccinates by aftertreatment withmaleic acid esters and optionally bases, and to the use of the sulfitedfatty compounds as leather auxiliaries.

2. Discussion of Related Art

Apart from tanning agents, oiling agents are the most importantauxiliaries for bringing out the character of leather. Oiling agentsdevelop their effect by fiber-insulating lubrication and byhydrophobicization.

The coating of the leather fibers with a fatty film reduces mutualfriction and, hence, improves the suppleness and elasticity of thetissue. This has positive effects on the tear strength of the leatherbecause, in an elastic material, many fibers--when subjected to tensilestressing--align themselves in the same direction as the tensile stressand then offer greater resistance to tearing than the same fibers in abrittle material. In addition, tanning effects are obtained through thehydrophobicization because hydrophobicization is accompanied by thedisplacement of water from the skin.

Vegetable and animal oils, fats and waxes and the hydrolysis,sulfonation, oxidation and hydrogenation products obtained therefrom bychemical conversion and, finally, mineral oiling agents are generallyused for oiling leather. More specifically:

Saponifiable fats and oils and natural waxes and resins belong to theesters. Oils and fats are understood by the leather expert to be estersof glycerol and fatty acids which are solid or liquid at roomtemperature. From the group of animal fats, train oils, fish oil, beeftallow and neat's foot oil in particular and, from the group ofvegetable fats, castor oil, rapeseed oil and linseed oil are used foroiling leather. In waxes and resins, the fatty acids are esterified withrelatively high molecular weight alcohols instead of glycerol. Examplesof waxes are beeswax, chinese wax, carnauba wax, montan wax and woolgrease. The most important resins include colophony, birch bark oil andshellac.

The chemical conversion of vegetable and animal fats gives productswhich are soluble in water and which, in addition, emulsifywater-insoluble fatty compounds to different extents. Known productsinclude, for example, the sulfonated water-soluble oils of variouskinds, train oils modified by oxidation which are known as degras ormoellon, the soaps formed in the hydrolysis of natural fats,hydrogenated fats and, finally, free fatty acids, such as stearic acid,as baking fats. Most animal and vegetable fats have a certain affinityfor leather which is considerably enhanced by the introduction orexposure of hydrophilic groups.

Mineral oiling agents are also important in leather manufacture. Thesehydrocarbons are similar to natural fats and oils in certain properties,but cannot be saponified. They are fractions from the distillation ofpetroleum which are known as mineral oil in liquid form, as vaseline inpaste-like form and as paraffin in solid form.

In many cases, however, unwanted stains known as fatty spew are formedover a period of time on the surface of tanned and oiled leather. Fattyspew is mainly formed on chrome-tanned leather after relatively short orprolonged storage as a white, often bloom-like coating which only coversindividual parts of the leather surface or even the entire leathersurface. Fatty spew is attributable to the secretion of solid fattycompounds from the leather. It can be caused by the natural fat presentin the leather or by fatty compounds which have been incorporated in theleather during the oiling process.

Fatty mixtures used to oil leather tend to form fatty spew in particularwhen they contain many free fatty acids. Free fatty acids generally havea higher melting point than their glycerides. The hydrolysis of fattycompounds during storage of the leather increases the risk of fatty spewaccordingly.

Soaps and fat liquors are hydrolyzed in chrome leather, especially ininadequately deacidified chrome leather, with release of fatty acids.Sulfonated oils and fats differ in their tendency to form fatty spew,the tendency to form fatty spew generally diminishing with the age ofthe leather [cf. J. Int. Soc. Leath. Trad. Chem. 379 (1952)].

Fatty spew is formed more easily, the greater the content of fattycompounds tending to form fatty spew in the leather. The quantity,composition and position of the fatty mixture of natural fat and fatliquor present in the leather are critical to the extent and compositionof the fatty spew. Loosely structured leather tends to form fatty spewless than leather with a dense fiber structure. Fatty spew is observedmore often at low temperatures than at relatively warm outsidetemperatures.

The crystalline fatty spew forms in the follicles and glandularchannels, small crystals initially being formed deep inside the follicleand gradually filling the entire follicle as relatively large fattycrystals which then spread out over the surface of the leather andcoalesce into a dense crystal film. Any fats containing stearin orpalmitin derivatives can cause crystalline fatty spew, the danger offatty spew increasing with increasing concentration [Ledertechn.Rundsch. 1 (1949)].

So-called neutral fats in particular, i.e. substances with no ionicgroups in the molecule which are suitable for oiling leather, forexample fats, waxes and hydrocarbons, tend to form fatty spew. Thoseneutral fats which are stearin and/or palmitin derivatives, such as forexample corresponding triglycerides or the free fatty acids, areparticularly critical in this regard.

Since oiling is virtually a compulsory step in the processing ofleather, but after tanning, to establish the required productproperties, it has become standard practice to use special syntheticoiling compositions with only a minimal tendency to form fatty spew.

One class of oiling agents widely used for this purpose are halogenatedcompounds, such as chlorinated hydrocarbons. Unfortunately, theincreasing ecological and toxicological requirements which compositionsentering the environment or coming into contact with the consumer areexpected to satisfy make this class of compounds increasinglyunattractive. The use of chloroparaffins as additives to fat liquoremulsions to prevent the formation of fatty spew on chrome-tannedpigskin is described, for example, by J. Golonka in Przegl. Skorzany42(2), 35 (cf. Chem. Abstracts 107(18):156865z).

EP-B 0 247 509 (Stockhausen) describes adducts of sulfuric acid or oleumwith unsaturated, alkoxylated and optionally epoxidized fats and oils.Unfortunately, products of this type generally have an unfavorably highelectrolyte content so that the salts are in danger of crystallizing outand impairing the quality of the treated leather.

In addition to reactions with oleum, sulfuric acid or gaseous sulfurtrioxide, sulfiting i.e. the addition of hydrogen sulfite ontounsaturated compounds, is particularly suitable for thehydrophilicization of fatty compounds. For example, A. Kuntzel reportsin this connection on the sulfiting of cod liver oil [Leder 8, 5 (1957)]while M. Mikula reports on the sulfiting of unsaturated fatty acid butylesters [Leder, Schuh, Lederwaren 21, 282 (1986)]. Although sulfitedfatty compounds show particularly favorable oiling behavior, they alsotend to form unwanted fatty spew. Another disadvantage is that theproducts have a pungent odor attributable to small amounts of unreactedhydrogen sulfite.

Accordingly, the methods from the prior art for preventing fatty speware not altogether satisfactory.

It is clear from the above context that there is a constant need in theleather industry for additives or oiling compositions which effectivelyprevent fatty spew so that the range of commercial products can beextended to allow a flexible response to the changing requirements ofthe market. More particularly, there is a need for ecologically orrather toxicologically safe additives and oiling compositions of whichthe use does not result in the unwanted formation of fatty spew.

Accordingly, the problem addressed by the present invention was toprovide new substances for oiling and hydrophobicizing leather whichwould be free from the disadvantages mentioned above.

DESCRIPTION OF THE INVENTION

The present invention relates to sulfited fatty compounds with a reducedcontent of free hydrogen sulfite which are obtained by blowingunsaturated fatty compounds in known manner, sulfiting the blown fattycompounds with sodium metabisulfite and then fixing unreacted hydrogensulfite as sulfosuccinic acid esters by aftertreatment with maleic acidesters and optionally bases.

It has surprisingly been found that the residual content of freehydrogen sulfite in blown sulfited fatty compounds can be significantlyreduced to levels below 1% by weight, based on the solids content of theproducts, if the crude products are aftertreated with maleic acid estersand optionally bases. The invention is based on the observation that thefree hydrogen sulfite reacts off quickly and almost completely with themaleic acid esters to form sulfosuccinic acid esters("sulfosuccinates"). The sulfited fatty compounds according to theinvention which contain sulfosuccinates show distinctly improvedperformance properties in relation to typical known products. Moreparticularly, their tendency to form fatty spew on leather surfaces issignificantly reduced, in addition to which the products aresubstantially odorless.

The present invention also relates to a process for the production ofsulfited fatty compounds with a reduced content of free hydrogensulfite, in which unsaturated fatty compounds are blown in known mannerand sulfited with sodium hydrogen sulfite, after which unreactedhydrogen sulfite is fixed as sulfosuccinic acid esters by aftertreatmentwith maleic acid esters and optionally bases.

Starting Materials

Fatty acid glycerides, fatty acid lower alkyl esters or mixtures thereofmay be used as the fatty compounds serving as starting materials for theproduction of the sulfited products.

a) Fatty acid glycerides are substances corresponding to formula (I):##STR1## in which --COR¹, COR² and COR³ and R³ CO independently of oneanother represent aliphatic acyl radicals containing 12 to 24 carbonatoms and 1, 2, 3 or 4 double bonds.

The fatty acid glycerides may be of synthetic origin or, moreparticularly vegetable or animal origin. Typical examples aretriglycerides which solely or predominantly contain palmitoleic acid,oleic acid, elaidic acid, petroselic acid, linoleic acid, linolenicacid, gadoleic acid, erucic acid, arachidonic acid and/or clupanodonicacid as fatty acid components. Preferred starting materials in thisregard are glycerol trioleate and also vegetable or animal fats and oilswhich have an iodine value of 50 to 150 and preferably 80 to 140.Without any claim to completeness, olive oil, olive kernel oil,sunflower oil from old and new plants, rapeseed oil from old and newplants, cottonseed oil, peanut oil, coriander oil, linseed oil, beeftallow and fish oil are mentioned as examples of suitable vegetable andanimal fats and oils. Commensurate with their nature, the vegetable andanimal fats and oils may also have saturated components providing theydo not exceed 50% by weight.

b) Fatty acid lower alkyl esters are substances corresponding to formula(II):

    R.sup.4 CO--OR.sup.5                                       (II)

in which R⁴ CO represents aliphatic acyl radicals containing 12 to 24carbon atoms and 1, 2, 3 or 4 double bonds and R⁵ represents linear orbranched alkyl radicals containing 1 to 4 carbon atoms.

Typical examples are ethyl, propyl, butyl and, more particularly, methylesters of palmitoleic acid, oleic acid, elaidic acid, petroselic acid,linoleic acid, linolenic acid, gadoleic acid, erucic acid, arachidonicacid and/or clupanodonic acid and the technical mixtures thereofobtained, for example, in the pressure hydrolysis of the vegetable andanimal fats and oils mentioned above. Oleic acid and/or linoleic acidmethyl ester is/are preferably used.

As mentioned above, the fatty acid glycerides and the fatty acid loweralkyl esters may be used both individually and in the form of mixtures.However, it has proved to be of particular advantage to sulfite mixturesof unsaturated fatty acid glycerides and unsaturated fatty acid loweralkyl esters together. The molar mixing ratio may vary over wide rangesand may be, for example, 1:5 to 5:1 and preferably 1:1 to 3:1.

Blowing and Sulfiting

The blowing of fatty compounds is a known process in which (atmospheric)oxygen is introduced into unsaturated fatty compounds at 100° to 150° C.The object of blowing is to increase the viscosity and stability of thefatty compounds by partial autoxidation [cf. ROEMPP, Chemielexikon,Thieme Verlag, Stuttgart, 9th Edition, Vol. II, page 1498 (1990)]. Inthe context of the process according to the invention, it has proved tobe of advantage to blow fatty acid compounds at 100° to 110° C. until anincrease in density of around 0.01 to 0.1 g/cm³ and preferably 0.02 to0.5 g/cm³ is reached.

Sulfiting can be carried out in known manner, sodium hydrogen sulfitebeing added onto the double bond of the unsaturated fatty compounds.Since sodium hydrogen sulfite is only stable in aqueous solution, sodiummetabisulfite (Na₂ SO₃) is used as the sulfiting agent. The unsaturatedfatty compounds and the sodium metabisulfite may normally be used in amolar ratio of 3:1 to 15:1 and preferably 5:1 to 10:1, based on thedouble bond equivalents in the unsaturated fatty compounds. It hasproved to be optimal to carry out the sulfiting step over a period of 1to 5 h and preferably 2 to 4 h at temperatures of 50° to 120° C. andpreferably 60° to 90° C.

Aftertreatment

According to the invention, hydrogen sulfite unreacted in the sulfitingstep is fixed as sulfosuccinic acid ester ("sulfosuccinate") byaftertreatment with a maleic acid ester.

Suitable maleic acid esters are compounds corresponding to formula (IV):

    R.sup.7 COO--CH═CH--COOR.sup.89                        (IV)

in which R⁷ is an alkyl and/or alkenyl radical containing 6 to 22 carbonatoms and R⁸ is hydrogen or an alkyl and/or alkenyl radical containing 6to 22 carbon atoms. Typical examples are monoesters or diesters ofmaleic acid or maleic anhydride with caproic alcohol, caprylic alcohol,capric alcohol, lauryl alcohol, myristyl alcohol, cetyl alcohol,palmitoleyl alcohol, stearyl alcohol, isostearyl alcohol, oleyl alcohol,elaidyl alcohol, petroselinyl alcohol, arachinyl alcohol, gadoleylalcohol, behenyl alcohol and erucyl alcohol and the technical mixturesthereof obtained, for example, in the hydrogenation of technical methylester fractions or aldehydes from Roelen's oxo synthesis. Maleic acidmonoesters of technical cocofatty alcohols or tallow fatty alcohols,more particularly oleyl alcohol, are preferably used.

The maleic acid esters may be used in quantities of 10 to 100 mole-%,based on the quantity of sodium metabisulfite used. The quantity usedwill normally be selected to correspond to the residual content of freehydrogen sulfite. Accordingly, a quantity of 15 to 30 mole-%, againbased on the quantity of metabisulfite used, is the preferred choice.However, with the performance properties of the product in mind, it maybe that the concentration of sulfosuccinate achieved by reaction of thefree hydrogen sulfite with the maleic acid ester is not sufficient. Inthis case, the percentage of free metabisulfite in the crude sulfitingproduct can be artificially increased, for example from 15% to 35% byweight, based on the solids content of the product. The expert will beable to take this aspect into account as a matter of course whenselecting the quantity of maleic acid ester without having to becomeinvolved in any inventive activity.

The aftertreatment of the crude sulfiting products with the maleic acidesters may be carried out in the presence of aqueous bases, such as forexample alkali metal or alkaline earth metal hydroxides or ammonia.Since it is the function of the base to neutralize free carboxyl groupsof the maleic acid or sulfosuccinic acid ester (where present), itsquantity will intentionally be selected so that a pH value at whichthere is no danger of saponification of the ester bonds is establishedin the product.

The aftertreatment may be carried out over a period of 0.5 to 5 h andpreferably 1 to 3 h at temperatures of 50° to 90° C. and preferably 70°to 85° C.

Industrial Applications

The sulfited fatty compounds provide leather with a pleasant supplenessand with resistance to moisture. They are substantially odorless, haveno tendency to form fatty spew and are readily biodegradable. Since freehydrogen sulfite does not adhere to the leather, but instead is washedout after the oiling treatment, the comparatively low electrolytecontent of the sulfited fatty compounds according to the invention is anadditional advantage from the ecological point of view.

Accordingly, the present invention also relates to leather oilingcompositions, more particularly for chrome-tanned leather, which maycontain from 1% to 99% by weight and preferably from 10% to 50% byweight of the sulfited fatty compounds according to the invention. Inaddition to the fatty compounds according to the invention, these oilingcompositions may contain other typical additives, such as for examplefatty acid esters and dialkyl ethers.

Finally, the present invention relates to the use of the sulfited fattycompounds according to the invention for the production of oiling andhydrophobicizing compositions, more particularly for chrome-tannedleather, in which they may be present in quantities of 1% to 99% byweight and preferably 10% to 50% by weight.

The following Examples are intended to illustrate the invention withoutlimiting it in any way.

EXAMPLES Example 1

A mixture of 250 g (0.2 mole) of fish oil (saponification value 130,iodine value 145) and 500 g (0.55 mole) of olive kernel oil(saponification value 185, iodine value 95) was introduced into a2-liter three-necked flask equipped with a stirrer, reflux condenser anddropping funnel and blown with air at 105° C. until an increase indensity of 0.03 g/cm³ (as measured at 20° C.) was obtained. The mixturewas then cooled to 60° C. and a solution of 90 g (0.9 mole) of sodiummetabisulfite in 170 ml of deionized water was added in portions throughthe dropping funnel. After the addition, the reaction mixture was heatedto 85° C. and stirred for another 2 h at that temperature. Unreactedhydrogen sulfite was then fixed as sulfosuccinic acid monoester by theaddition of 75 g (0.2 mole) of maleic acid monooleyl ester and 20 g(0.85 mole) of ammonia in the form of a 50% by weight aqueous solution.The residual content of free hydrogen sulfite was 0.5% by weight, basedon the solids content of the sulfited product.

Example 2

A mixture of 250 g (0.2 mole) of fish oil, 250 g (0.28 mole) of glyceroltrioleate and 250 g (0.84 mole) of olive kernel oil fatty acid methylester was blown at 105° C. as in Example 1 until an increase in densityof 0.03 g/cm³ was obtained and was then sulfited with 68 g (0.68 mole)of sodium metabisulfite in 120 ml of water. Unreacted hydrogen sulfiteand another 22 g (0.22 mole) of sodium metabisulfite, which had beenadded to the fully reacted reaction mixture, were then fixed assulfosuccinic acid monoester by addition of 75 g (0.2 mole) of maleicacid monooleyl ester and 20 g (0.85 mole) of ammonia in the form of a25% by weight aqueous solution. The residual content of free hydrogensulfite was 0.9% by weight, based on the solids content of the sulfitedproduct.

I claim:
 1. Sulfited fatty compounds having a reduced content of freehydrogen sulfite prepared by blowing unsaturated fatty compounds in anoxygen atmosphere at 100° C. to 180° C., sulfiting the blown fattycompounds with sodium metabisulfite, and subsequently fixing unreactedhydrogen sulfite as sulfosuccinic acid ester by aftertreatment withmaleic acid esters, and optionally, a basic material.
 2. The process ofproducing sulfited fatty compounds having a reduced content of freehydrogen sulfite, comprising blowing unsaturated fatty compounds in anoxygen atmosphere at 100° C. to 150° C., sulfiting the blown fattycompound with sodium metabisulfite, and fixing unreacted hydrogensulfite as sulfosuccinic acid ester by aftertreatment with maleic acidesters, and optionally, a basic material.
 3. A process as in claim 2wherein said unsaturated fatty compounds are selected from the groupconsisting of fatty acid glycerides, fatty acid lower alkyl esters, andmixtures thereof.
 4. A process as in claim 3 wherein said fatty acidglycerides correspond to formula (I): ##STR2## in which COR¹, COR² andCOR³ independently of one another represent aliphatic acyl radicalscontaining 12 to 24 carbon atoms and 1, 2, 3 or 4 double bonds.
 5. Aprocess as in claim 3 wherein said fatty acid lower alkyl esterscorrespond to formula (II):

    R.sup.4 CO--OR.sup.5                                       (II)

in which R⁴ CO represents alipatic acyl radicals containing 12 to 24carbon atoms and 1, 2, 3 or 4 double bonds, and R⁵ represents linear orbranched alkyl radicals containing 1 to 4 carbon atoms.
 6. A process asin claim 2 wherein said unsaturated fatty compounds are blown in saidoxygen atmosphere until an increase in density of 0.01 to 0.1 g/cm³ isobtained.
 7. A process as in claim 2 wherein said unsaturated fattycompounds and said sodium metabisulfite are present in a molar ratio of3:1 to 15:1, based on double bond equivalents in said unsaturated fattycompounds.
 8. A process as in claim 2 wherein said maleic acid esterscorrespond to formula (IV):

    R.sup.7 COO--CH═CH--COOR.sup.8                         (IV)

in which R⁷ is an alkyl or alkenyl radical containing 6 to 22 carbonatoms and R⁸ is hydrogen or an alkyl or alkenyl radical containing 6 to22 carbon atoms.
 9. A process as in claim 2 wherein from 10 to 100mole-%, based on the quantity of sodium metabisulfite used to sulfitesaid blown fatty compounds of said maleic acid esters is present to fixsaid untoacted hydrogen sulfite as sulfosuccinic acid ester.
 10. Aprocess as in claim 2 wherein said basic material is selected from thegroup consisting of alkali metal and alkaline earth metal hydroxides,and ammonia in the form of aqueous solutions.
 11. A process as in claim2 wherein said aftertreatment is carried out at a temperature of 50° C.to 90° C.
 12. A leather treating composition containing sulfited fattycompounds having a reduced content of free hydrogen sulfite prepared byblowing unsaturated fatty compounds in an oxygen atmosphere at 100° C.to 150° C., sulfiting the blown fatty compounds with sodiummetabisulfite, and subsequently fixing unreacted hydrogen sulfite assulfosuccinic acid ester by aftertreatment with maleic acid esters, andoptionally, a basic material.
 13. A leather treating composition as inclaim 12 wherein said unsaturated fatty compounds are selected from thegroup consisting of fatty acid glycerides, fatty acid lower alkylesters, and mixtures thereof.
 14. A leather treating composition as inclaim 13 wherein said fatty acid glycerides correspond to formula (I):##STR3## in which COR¹, COR² and COR³ independently of one anotherrepresent aliphatic acyl radicals containing 12 to 24 carbon atoms and1, 2, 3 or 4 double bonds.
 15. A leather treating composition as inclaim 13 wherein said fatty acid lower alkyl esters correspond toformula (II):

    R.sup.4 CO--OR.sup.5                                       (II)

in which R⁴ CO represents aliphatic acyl radicals containing 12 to 24carbon atoms and 1, 2, 3 or 4 double bonds, and R⁵ represents linear orbranched alkyl radicals containing 1 to 4 carbon atoms.
 16. A leathertreating composition as in claim 12 wherein said unsaturated fattycompounds are blown in said oxygen atmosphere until an increase indensity of 0.01 to 0.1 g/cm³ is obtained.
 17. A leather treatingcomposition as in claim 12 wherein said blown fatty compounds and saidsodium metabisulfite have been reacted in a molar ratio of 3:1 to 15:1,based on double bond equivalents in said fatty compounds.
 18. A leathertreating composition as in claim 12 wherein said maleic acid esterscorrespond to formula (IV):

    R.sup.7 COO--CH═CH--COOR.sup.8                         (IV)

in which R⁷ is an alkyl or alkenyl radical containing 6 to 22 carbonatoms and R⁸ is hydrogen or an alkyl or alkenyl radical containing 6 to22 carbon atoms.
 19. A leather treating composition as in claim 12wherein from 10 to 100 mole-%, based on the quantity of sodiummetabisulfite used to sulfite said blown fatty compounds, of said maleicacid esters is present to fix said unreacted hydrogen sulfite assulfosuccinic acid ester.
 20. A leather treating composition as in claim12 wherein said basic material is selected from the group consisting ofalkali metal and alkaline earth metal hydroxides, and ammonia in theform of aqueous solutions.
 21. A leather treating composition as inclaim 12 wherein said aftertreatment is carried out at a temperature of50° C. to 90° C.